Question
Which of the following reactions is an example of nucleophilic substitution reaction?
A.
$$RX + KOH \to ROH + KX$$
B.
$$2\,RX + 2\,Na \to R - R + 2NaX$$
C.
$$RX + {H_2} \to RH + HX$$
D.
$$RX + Mg \to RMgX$$
Answer :
$$RX + KOH \to ROH + KX$$
Solution :
$$\eqalign{
& KOH \to {K^ + } + O{H^ - } \cr
& RX + \mathop {O{H^ - }}\limits_{{\text{Nucleophile}}} \to R - OH + {X^ - } \cr} $$
$$O{H^ - }$$ is a stronger nucleophile than halogen. So it easily replace the weaker nucleophile.
Nucleophiles are either negative charge or lone pair of electrons bearing species, e.g. $$O{H^ - },\ddot N{H_3},\,$$ etc.